Implantable Device Utilizing Arterial Deformation

ABSTRACT

The present invention relates to deforming a patient&#39;s artery. In a preferred embodiment, the deformation pressure is applied to the outer wall of the artery.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.12/044,853, filed on Mar. 7, 2008 and entitled “Heart Assist DeviceUtilising Aortic Deformation;” which is a continuation of U.S. Pat. No.7,347,811, filed on Nov. 5, 2003, issued on Mar. 25, 2008, and entitled“Heart Assist Device Utilising Aortic Deformation;” which claimspriority to Australian Provisional Application No. 2002952691, filed onNov. 15, 2002. The priority of these prior applications is expresslyclaimed, and the disclosures of the prior applications are herebyincorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to counterpulsation heart assistdevices, systems and methods and, more particularly, to heart assistdevices utilizing aortic deformation and/or aortic resection.

BACKGROUND OF THE INVENTION

The concept of providing counter-pulsation support for the failing hearthas been known since the pioneering work of Kantrowitz.Counter-pulsation causes displacement of a volume of a patient's bloodin the patient's aorta while the patient's heart is dilating in diastoleand after the aortic valve has closed. This assists to move blood aroundthe patient's peripheral vasculature as well as into the coronaryarteries. The timed volume displacement in the aorta on the blood withinthe aorta just in advance of systolic ejection of blood from the heartreduces the afterload on the heart, by causing a transient low pressureabove the aortic valve

It is known from the use of counter-pulsation in Intra-Aortic BloodPumps (IABPs) that counter-pulsation can provide short term support forthe failing heart. These devices require a balloon to be insertedpercutaneously into the descending aorta. The balloon is inflated anddeflated in counter-pulsation with the heart by the transmission of agas, usually helium, between the balloon and a bedside console. Thesedevices suffer from the problem that there is a high risk ofthrombo-embolism if the balloon remains in the vasculature for aprolonged period, which can lead to ischemic leg complications.

There have been a number of attempts to provide counter-pulsationsupport for the failing heart by applying counter-pulsation pressure tothe outside of the aorta. These proposals are contained in the followingpatent specifications:

PCT 99/04833 U.S. Pat. No. 4,014,318 U.S. Pat. No. 4,583,523 U.S. Pat.No. 4,979,936 U.S. Pat. No. 6,030,336 U.S. Pat. No. 6,045,496

A similar arrangement is described by Furman, New York Journal ofMedicine, Aug. 1, 1970, pp 1964-1969. In all of these arrangements meansare provided to surround, or at least substantially surround, the aortaand to apply a squeezing pressure substantially uniformly around thecircumference of the aorta. The present inventors have found that thereare substantial advantages if the counter-pulsation pressure is appliedto only a part of the circumference of the aorta.

It is also known to resect a part of the aorta for the purpose ofinserting a patch or other graft into the aorta and to cause such patchor graft to counterpulsate. Such a system is described in the followingpatent specifications:

PCT 01/13974 U.S. Pat. No. 4,630,597

The device described in these specifications is for insertion into thedescending aorta which is straight. There is no suggestion of how todeal with the more complex issues that arise in placing the device intothe ascending aorta which is curved along its length.

It would be desirable to have a heart assist device, which may or maynot be blood contacting that could provide assistance to the heartfunction with reduced risk to the patient and/or of device malfunctionthan prior art devices.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention provides a device for assisting thefunctioning of the heart of a patient, the device including:

an aortic compression means adapted, when actuated, to compress anaorta; and

motive means to periodically actuate, and de-actuate, the aorticcompression means in counter-pulsation with the patient's heart rhythm,

wherein the aortic compression means is adapted to compress only aportion of the circumference of the aorta.

Preferably, the aortic compression means is adapted to compress lessthan half of the circumference of the aorta.

In one form, the aortic compression means is a mechanical device driven,upon actuation, into compressive contact with the exterior of the aorta.In another form, the aortic compression means includes a flexiblemembrane, which may be elastic or inelastic, driven, upon inflation,into compressive contact with the exterior of the aorta.

The aortic compression means is preferably adapted to compress only aportion of the circumference of the ascending aorta, most preferablyonly the radially outer side of the ascending aorta.

In a second aspect, the present invention provides, in a heart assistdevice of the type which induces counter-pulsation of an artery in thevasculature of a patient, the improvement comprising the application ofa counter-pulsation pressure to the exterior of the artery such that theartery is caused to flex along a continuous line which increases inlength as the counterpulsation pressure applied to the artery increases.

The line preferably has the shape of a conic section.

In a third aspect, the present invention provides, in a heart assistdevice of the type which induces counterpulsation of an artery in thevasculature of a patient, the improvement comprising the application ofa counterpulsation pressure to the exterior of the artery such that theartery is caused to compress substantially without stretching orbunching.

In a fourth aspect, the present invention provides, in a heart assistdevice which includes aorta deformation means to apply acounter-pulsation pressure to the ascending aorta of a patient,characterised in that the aorta deformation means applies a deformingforce to the outside of the radially outer side of the curvature in theascending aorta and that the aorta deformation means induces in theaorta a smoothly curved ovate depression as it moves to a position ofmaximum deformation of the aorta.

In a fifth aspect, the present invention provides, in a heart assistdevice which includes aorta deformation means to apply acounter-pulsation pressure to the descending aorta of a patient,characterised in that the aorta deformation means applies a deformingforce to the outside of the descending aorta and that the aortadeformation means induces in the aorta a smoothly curved circulardepression as it moves to a position of maximum deformation of theaorta.

In a sixth aspect, the present invention provides, in a heart assistdevice including artery deformation means adapted to periodically applya deforming force to a curved artery in a direction substantially normalto a tangent to the radially outer surface of the longitudinal curve inthe artery, the deforming force being such that the artery isprogressively deformed along a line which lies in a plane runningthrough the artery, the plane moving radially inwardly through theartery as the deformation increases.

In a seventh aspect, the present invention provides, in acounter-pulsation type heart assist device adapted for insertion intothe wall of the ascending aorta of a patient, the device including aninflatable balloon extending around less than one half of thecircumference of the aorta and means to inflate the balloon incounter-pulsation with the heart of a patient into which the device hasbeen inserted, the balloon having a substantially inelastic outer layerand an inner layer with a shape which is, when the balloon is deflated,smoothly curved and facing directly inwardly into the lumen of theascending aorta of the patient into which the device has been inserted.Alternatively the device may be applied to the outside of the wall ofthe aorta.

In an eighth aspect, the present invention provides, in a heart assistdevice adapted to apply a counter-pulsation force to a patch insertedinto at least the radially outer arc of the ascending aorta the forcebeing applied to the radially outer arc of the aorta to cause the wallor the patch to invaginate, the device being characterised in that itincludes deformation means for the application of the pressure to thewall or patch which deformation means has, when the wall or patch isfully invaginated, a shape which is substantially a mirror image of thesection of the wall or patch which has been invaginated before it was soinvaginated. Alternatively the device may be applied to the outside ofthe wall of the aorta.

The above embodiment is designed to apply a compressive force to theartery so as to cause the blood therein to be displaced while causingthe minimum trauma to the vessel. In preferred embodiments of theinvention the compression of the ascending aorta is induced in a waywhich reduces the enclosed volume of the aorta while not undulystretching or bunching the wall of the aorta.

The deformation of the artery may be induced by a balloon or by a rigidobject. In either case the object inducing the deformation shall be soshaped that the desired form of deformation of the artery is achieved.In the case of a balloon, the balloon should be so shaped that as it isinflated it will take on a shape similar to that which is desired to beachieved in the artery. It must also be so placed on the artery that thedesired smoothly flexing and smoothly shaped deformation is achieved. Inthe case of a rigid object the object should initially be of anappropriate shape to induce the desired deformation of the artery as itis advanced towards the artery either along a linear path or an arcuateone. Preferably, the deforming object will be moved into the artery in adirection which is radial of the artery and either at right angles toits axis, if it is straight, or at right angles to a tangent to theradially outer side of the artery, if it is curved.

Preferably, the deformation of the vessel does not extend around morethan 180 degrees of the circumference of the vessel, more preferably nomore than 160 degrees and even more preferably not more than 140 degreesand most preferably between 100 and 140 degrees. The cuff or balloon mayextend further around the aorta than the preferred amount, however, theactive deformation of the aorta preferably only extends around an arc ofthe aorta within the above limits. The desire of this design preferenceis to avoid the inside surface of the deformed vessel touching theinside surface of the vessel diametrically opposite the deformation.

In preferred embodiments the deformational force will be applieddirectly to the arterial wall. However, if desired a layer of anysuitable material may be placed between the deformational member and thewall. In an alternative embodiment of the invention a section of thearterial wall may be resected and a patch applied which substantiallyreplicates the shape of the native artery and the deformational forceapplied to the outside surface of that patch. In this embodiment of theinvention the patch is applied to the radially outer arc of theascending aorta and preferably has a shape similar to the section of theascending aorta which has been removed.

The heart assist device of the present invention allows, at least inpreferred embodiments, partial unloading of the heart and augmenting ofthe cardiac output of the heart.

After use, if the heart has recovered, the device can be left in situ,in an inactive state, until needed again. The device can also be used toadminister on-demand, spaced-apart sessions of counterpulsation fortreatment or relief from chronic myocardial ischemia and/or heartfailure.

In a preferred form of the invention, the device is adapted forattachment to the ascending aorta. An upper mid-line sternotomy providessurgical access to the ascending aorta. Alternatively, a thoracotomy maybe used to place the device on the descending aorta.

The motive means referred to above can be any means that is capable ofcyclically introducing fluid, and withdrawing fluid, from an inflatablebladder, balloon or cuff. The motive means can include or be associatedwith means for detecting speed and completeness of the filling andemptying, and for monitoring the delivered fluid pressure. The motivemeans can also act to record the ECG, having electrodes positioned onthe housing or as separate wires attached to body tissues.

In a further aspect, the present invention provides a method forimproving cardiac performance in a subject, the method including thesteps of:

implanting a device in accordance with any one of the preceding aspectsof the invention fully within the thoracic cavity of a subject;

actuating the motive means to periodically introduce the fluid into thespace in synchrony with the diastolic period to reduce the interiorvolume of the aorta; and

alternating the period of actuation with periods of deactivation of themotive means to periodically withdraw the fluid from the space insynchrony with the commencement of the systolic period, thereby allowingthe portion of the aorta adjacent the device to return to normalinterior volume.

The method may include the step of resecting a portion of the ascendingaorta in the shape of a toroidal truncate and sealingly attaching theperiphery of the device to the periphery of the opening aorta.

In another aspect, the present invention provides a device for assistingthe functioning of the heart of a patient, the device including:

a patch device sealingly attachable to the ascending aorta;

a flexible membrane sealingly attached to at least part of the interiorof the patch device and defining an inflatable space adjacent theinterior of the patch device; and

motive means to periodically introduce into, and withdraw from, thespace a fluid, in counter-pulsation with the patient's heart rhythm.

The patch device is preferably attachable to the radially outer side ofthe ascending aorta. In one form, the patch device is attachable to theperiphery of an opening in the ascending aorta formed by resecting aportion of the aorta. The membrane has a shape substantially replicatingthat of the interior surface of the resected portion of the aorta. Theflexible membrane preferably also substantially replicates the shape ofthe interior of the patch device when the fluid is withdrawn from thespace. It is believed that this design feature will reduce the incidenceof thrombo-embolism by presenting, when deflated, a blood flow pathwithout regions that would cause sluggish blood flow. The patch deviceis preferably in the shape of a truncated portion of a torus. The aortais preferably resected along a line on the radially outer side, orpassing through, the diameter of the mid point cross section of theaorta. The membrane, when the fluid is introduced into the space, ispreferably expanded towards, but not abutting, the adjacent interiorwall of the aorta.

In another form, the patch device is attachable to the ends of the aortaformed by removing a length of the aorta. The patch device preferablyincludes a truncated substantially toroidal portion with an externallyfacing hump that forms the inflatable space. The membrane is preferablyattached to the patch device about the periphery of the hump. Thesurface of the membrane remote the space preferably has a shape, whenthe fluid is withdrawn from the space, substantially replicating that ofthe interior surface of the removed portion of the aorta. The flexiblemembrane preferably also substantially replicates the shape of theinterior of the hump when the fluid is withdrawn from the space. Thehump is preferably disposed external to a line on the radially outerside, or passing through, the diameter of the mid point cross section ofthe aorta. The membrane, when the fluid is introduced into the space, ispreferably expanded close to, but not abutting, the adjacent interiorwall of the aorta.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexamples only, with reference to the accompanying drawings in which

FIG. 1 is a cross sectional ventral view of the aorta of a patient witha first embodiment of a device for assisting the functioning of a heart;

FIG. 2 is a schematic lateral view of the device shown in FIG. 1;

FIG. 3 is a ventral view of the aorta of a patient showing a series ofplanes through the aorta in which lines of flexure of the aortic wallwill lie during application of a deforming force to the aorta;

FIG. 4 is cross sectional view along line 4-4 through the aorta of FIG.3 showing a sequence of shapes assumed by the aortic wall as it isdeformed;

FIG. 5 is a part longitudinal cross- sectional view through the aorta ofFIG. 3 along line 5-5 of FIG. 6, showing a sequence of shapes assumed bythe aortic wall as it is deformed;

FIG. 6 is a lateral view from the right side of the aorta of FIG. 3,showing a sequence of lines of flexure as the aorta is deformed;

FIG. 7 is a schematic side view of an ascending aorta showing aresection line;

FIG. 8 is a schematic side view of the aorta shown in FIG. 7 afterresection of a portion of the aorta;

FIG. 9 is a schematic side view of another embodiment of a device forassisting the functioning of the heart with a withdrawn internalmembrane;

FIG. 10 is a schematic side view of the device shown in FIG. 9 with anexpanded membrane;

FIG. 11 is a schematic side view of the aorta shown in FIG. 8 aftersurgical attachment of the device shown in FIGS. 9 and 10 with themembrane shown in withdrawn and expanded positions;

FIG. 12 is a schematic cross sectional end view of the aorta and deviceshown in FIG. 11;

FIG. 13 is a schematic cross sectional view of an aorta of reduced sizewith a resected portion;

FIG. 14 is a cross sectional end view of the aorta of FIGS. 13 and 15after surgical attachment of a further embodiment of device forassisting in the functioning of the heart;

FIG. 15 is a schematic front view of the resected aorta shown in FIG.13;

FIG. 16 is a schematic front view of the aorta and device shown in FIG.15;

FIG. 17 is a schematic side view of an ascending aorta showing analternatively positioned resection line;

FIG. 18 is a cross sectional ventral view of the aorta of a patient witha further embodiment of a device for assisting the functioning of aheart.

DETAILED DESCRIPTION

FIG. 1 is a schematic side view of an ascending aorta 10 and a heartassist device 16 in accordance with an embodiment of the invention. Thedevice 16 has a relatively inelastic, preferably plastic, shell 17 and aflexible membrane 18 sealingly attached to the periphery of the shell17. The membrane 18 defines an inflatable space 19 between it and theinterior of the shell 17. The shell 17 also has an inlet/outlet port 20which is adapted for connection to a motive means that can periodicallyintroduce, and withdraw, a fluid (eg. a gas such as helium or a liquidsuch as a saline solution or an oil) to and from the space 19 incounter-pulsation with the patient's heart rhythm. The membrane 18 has ashape which is, when deflated, smoothly curved and facing directlyinwardly towards the lumen of the ascending aorta 10.

A relatively inelastic wrap 21 is used to hold the device 16 in theposition shown on the radially outer side of the ascending aorta 10.

The solid line 18 illustrates the position of the membrane 18 relativeto the shell 17 when fluid has been withdrawn from the space 19 and themembrane 18 has been retracted. In this position the radially outerexternal side wall 10 e of the aorta 10 is in its normal or deflatedposition allowing maximum blood flow there through.

The phantom line 18 illustrates the position of the membrane 18 relativeto the shell 17 after fluid has been introduced into the space 19 andthe membrane 18 has been expanded. When the membrane 18 is expanded inthis way, the aorta external wall 10 e is compressed and inwardlydeformed until it is close to, but not abutting, the opposite interiorwall of the aorta 10 r.

The membrane 18 is sized and positioned to compress only a portion ofthe circumference of the radially outer side of the ascending aorta 10.More particularly, the membrane 18 compresses only about 140 degrees ofthe circumference of the aorta 10.

FIGS. 3 to 6 show, in various orientations and views, the shape theexternal wall 10 e of the ascending aorta 10 assumes from initialdeformation (line A) through to maximum deformation (line E). The linesA to E show the exterior of the aorta 10 flexing along a continuousline, that preferably has the shape of a conic section, which increasesin length as the counter pulsation pressure applied to the arteryincreases. An advantage of flexing the aorta in this manner is that itis caused to compress substantially without stretching, which reducesthe likelihood of damage. Also the line of flexure is constantly movingso that one line of the aorta 10 is not being constantly exposed toflexural movement. Put another way, the exterior of the aorta isdeformed to induce a smoothly curved ovate depression as it movestowards a position of maximum deformation (line E) of the aorta 10. Inan alternative embodiment, a smoothly curved circular depression can beformed in the aorta.

The lines A to E also show how the artery is progressively deformedalong a line which lies in a plane running through the artery 10, thatplane moving radially inwardly through the artery as the deformationincreases.

The deformation described above can be caused to occur in many otherdifferent ways. For example, in another embodiment, deformation can becaused by a patch device inserted into the radially outer arc of theascending aorta. In such an embodiment, the device includes a means forapplying pressure to the wall or patch which, when the wall or patch isfully invaginated, forms a shape which is a mirror image of the sectionof the wall or patch which as been invaginated before it was soinvaginated.

Another embodiment of a device for assisting the functioning of a heartaccording to the present invention will now be described in relation toFIGS. 7 to 12. Like reference numerals will be used to indicate likefeatures used in describing to the preceding embodiment.

FIG. 7 is a schematic side view of a portion of ascending aorta 10. Line12 is a resection line passing through the diameter of the midpointcross section of the aorta 10 (see also FIG. 12).

FIG. 8 is a schematic view of the resected aorta 10 r after cutting theaorta 10 along the resection line 12 and removal of a resected portion14.

FIG. 9 is a schematic side view of a heart assist device 16 inaccordance with another embodiment of the invention. The device 16 has arelatively inelastic, preferably plastic, shell 17 and a flexiblemembrane 18 sealingly attached to the periphery of the shell 17. Themembrane 18 defines an inflatable space 19 between it and the interiorof the shell 17. The shell 17 also has an inlet/outlet port 20 which isadapted for connection to a motive means that can periodicallyintroduce, and withdraw, a fluid (eg. a gas such as helium or a liquidsuch as a saline solution or an oil) to and from the space 19 incounter-pulsation with the patient's heart rhythm.

FIG. 9 illustrates the position of the membrane 18 relative to the shell17 when fluid has been withdrawn from the space 19 and the membrane 18has been retracted (18 r in FIGS. 11 and 12). FIG. 10 illustrates theposition of the membrane 18 relative to the shell 17 after fluid hasbeen introduced into the space 19 and the membrane 18 has been expanded(18 e in FIGS. 11 and 12). When the membrane 18 is expanded it is closeto, but not abutting, the opposite interior wall of the aorta 10 r.

The shell 17 has a peripheral edge of common shape to the opening formedin the aorta 10 r after removal of the resected portion 14. This permitsthe device 16 to be attached to the resected aorta 10 r by stitchingbetween the periphery of the shell 17 and the periphery of the openingin the resected aorta 10 r, as indicated by stitches 22 in FIG. 11.

The motive means (not shown) include a fluid reservoir and a pump meansadapted to pump the fluid from, the fluid reservoir to the port 20, andthus the space 19 between the interior of the shell 17 and the flexiblemembrane 18, and then withdrawn same, to expand (18 e) and retract (18r) the membrane 18 as indicated in FIGS. 5 and 6. Suitable implantablefluid reservoirs and pump means are disclosed in the applicant'sinternational PCT patent application Nos. PCT/AUOO/00654 andPCT/AUO2/00974, which are hereby incorporated by cross reference.

More particularly, in use, the motive means is periodically actuated tointroduce fluid into the space 19 in synchrony with the diastole periodto reduce the interior volume of the aorta 10 r and thereby provideadditional pumping of the blood in the aorta 10 r to assist thefunctioning of the heart. This introduction of fluid is alternated withperiodic withdrawal of the fluid from the space 19 to allow the aorta 10r to return to its normal interior volume. As described above, theintroduction of fluid expands the membrane 18 to be close to, but notabutting, the opposite interior wall of the aorta 10 r. This maximisespumping volume without risk of the membrane 18 contacting and damagingthe aorta 10 r.

It will be appreciated that the heart assist device 16 includes acomponent, namely the membrane 18, which is blood contacting. However,the previously described disadvantages of blood contacting are minimisedby the present invention as when the fluid is withdrawn from the space19 the membrane 18 is drawn into a shape substantially replicating theoriginal (now resected) aorta wall. As a result, no eddies or pocketsare introduced into the blood flow path that may disrupt blood flow whenthe device 16 is not activated thereby substantially reducing clot risk.

Also, if the heart recovers the device 16 can be deactivated with themembrane 18 in the retracted position (see FIGS. 9 and 18 r in FIGS. 11and 12) allowing natural blood flow there through. In this connection,it should also be noted that heart assist devices have been proposedthat function in parallel to the aorta and which receive the fulldiverted flow of blood originally intended for to the aorta. Thesedevices can not be deactivated unlike the device according to thepresent invention.

Further, by installing the device 16 in a position vacated by theresected portion 14 of the aorta 10 it achieves a relatively highpumping volume for a relatively low device volume.

The flexible membrane 18 is preferably manufactured from a polyurethaneor a polyurethane-polysiloxane block co-polymer material or othersimilar material, which encourages ingrowth of the passing blood cellsand can eventually create a new “natural” cell lining.

The device according to the present invention is also particularlyadvantageous for use in patients whose aortas have become diseased asthe device can be implanted in place of the resected damaged section.

A further embodiment of the device for assisting the functioning of aheart according to the present invention will now be described inrelation to FIGS. 13 to 16. Like reference numerals will be used toindicate like features used in describing to the preceding embodiment.This embodiment is particularly suitable for use in patients having anaturally small aorta or an aorta that has shrunk through heart diseaseor the like.

FIG. 13 is a schematic cross sectional end view of a reduced diameterresected aorta 10 r showing resection line 12 and resected portion 14.The periphery of the opening formed by removing the resected portion 14is denoted 24 in FIG. 15. FIG. 14 shows the resected aorta 10 r afterits included angle a has been increased to {acute over (α)}+ so as toopen or stretch out the opening 24 in the aorta 10 r. Such stretchingallows the attachment of a heart assist device 16 of a similar size tothat used in a healthy aorta. In this way, the effective cross sectionof the aorta available for pumping by the membrane 18 can be increased.For example, from about 707 mm² at an original diameter of 30 mm toabout 1257 mm² at a stretched diameter of 40 mm. This results in acorresponding increase in the pumping volume of the aorta 10 r.

FIG. 17 is a schematic side view of an ascending aorta 10 showing analternatively positioned resection line 12. In this form, the resectionline 12 is angled towards the top of the aorta 10 to resect the upper,radially outer arc of the aorta 10.

A further embodiment of a device for assisting the functioning of aheart according to the present invention will now be described inrelation to FIG. 18. Like reference numerals will be used to indicatelike features used in describing to the preceding embodiments.

In FIG. 18 the heart assist device is a patch device 16 attachable tothe ends of the aorta 10, at stitches 22, formed by removing a length ofthe aorta. The patch device 10 is in the general shape of a truncatedtoroid with an externally facing hump that forms the inflatable space19. The membrane 18 is attached to the patch device 16 about theperiphery of the hump. The hump is disposed external to a line on theradially outer side, or passing through, the diameter of the mid pointcross section of the aorta 10.

The flexible membrane 18 substantially replicates the shape of theinterior of the hump when the fluid is withdrawn from the space 19. Themembrane 18, when the fluid is introduced into the space 19, is expandedclose to, but not abutting, the adjacent interior wall of the aorta, asis shown in phantom line.

Whilst the above embodiments have been described in relation tocompressing the radially outer wall of the aorta, it would beappreciated by a person skilled in the art that other portions of theaorta can be deformed or other arteries can be deformed to assist inheart functions.

The heart assist devices described above are suitable for short and/orlong term treatment for heart failure and/or myocardial ischemia.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

What is claimed is:
 1. An implantable device, comprising: (a) asubstantially inelastic shell comprising an outer surface and an innersurface, wherein the shell is curved such that the inner surface issubstantially concave; (b) a flexible membrane sealingly coupled to theshell, wherein an inflatable space is defined between the flexiblemembrane and the inner surface, wherein the flexible membrane has adeflated configuration and an inflated configuration, wherein theinflated configuration is a smoothly curved ovate projection; (c) a portassociated with the outer surface of the shell, wherein an interiorportion of the port is in fluid communication with the inflatable space;and (d) a wrap coupled to the outer surface of the shell, the wrapconfigured to be removeably positionable around a portion of a patient'sartery such that the flexible membrane is configured to be held againstthe artery, wherein the device has no other component or structure forholding the device against the artery, wherein the shell is configuredto extend around only a portion of the circumference of the artery. 2.The implantable device of claim 1, wherein the flexible membrane issubstantially inelastic.
 3. The implantable device of claim 1, whereinthe port is configured to be coupleable to a motive component.
 4. Theimplantable device of claim 1, wherein a fluid is disposed within theinflatable space in the inflated configuration.
 5. The implantabledevice of claim 4, wherein the fluid is a liquid.
 6. The implantabledevice of claim 1, wherein the smooth curved ovate projection isconfigured to cause the artery to flex into a conic shape defined by acontinuous line.
 7. The implantable device of claim 1, wherein thesmooth curved ovate projection is configured to cause the artery to flexsubstantially without stretching a wall of the artery.
 8. An implantabledevice, comprising: (a) a substantially inelastic shell comprising anouter surface and an inner surface, wherein the shell is curved suchthat the inner surface is substantially concave; (b) a flexible membranesealingly coupled to the shell, wherein an inflatable space is definedbetween the flexible membrane and the inner surface, wherein theflexible membrane has a deflated configuration and an inflatedconfiguration, wherein the inflated configuration is a smoothly curvedoval projection; (c) a port associated with the outer surface of theshell, wherein an interior portion of the port is in fluid communicationwith the inflatable space; and (d) a wrap coupled to the outer surfaceof the shell, the wrap configured to be removeably positionable around aportion of a patient's artery such that the flexible membrane isconfigured to be held against an outer side of the artery, wherein thedevice has no other component or structure for holding the deviceagainst the artery, wherein the smooth curved oval projection isconfigured to cause the outer side of the artery to progressively deformsubstantially without stretching a wall of the artery, wherein the shellis configured to extend around only a portion of the circumference ofthe artery.
 9. The implantable device of claim 8, wherein the flexiblemembrane is substantially inelastic.
 10. The implantable device of claim8, wherein the port is configured to be coupleable to a motivecomponent.
 11. The implantable device of claim 8, wherein a fluid isdisposed within the inflatable space in the inflated configuration. 12.The implantable device of claim 8, wherein the smooth curved ovateprojection is further configured to cause the outer side of the arteryto progressively deform into a conic shape defined by a continuous line.13. An implantable device, comprising: (a) a shell comprising an outersurface and an inner surface, wherein the shell is curved such that theinner surface is substantially concave; (b) a substantially inelasticflexible membrane sealingly coupled to the shell, wherein an inflatablespace is defined between the flexible membrane and the inner surface,wherein the flexible membrane has a deflated configuration and aninflated configuration, wherein the inflated configuration is a smoothlycurved oval projection, and further wherein the flexible membrane isconfigured to be positionable against an outer side of a patient'sartery; (c) a port associated with the outer surface of the shell,wherein an interior portion of the port is in fluid communication withthe inflatable space; and (d) a wrap coupled to the outer surface of theshell, wherein the wrap is removeably positionable around a portion ofthe artery such that the wrap holds the device against an outer side ofthe artery, wherein the device has no other component or structure forholding the device against the artery, wherein the shell is configuredto extend around only a portion of the circumference of the artery. 14.The implantable device of claim 13, wherein the port is configured to becoupleable to a motive component.
 15. The implantable device of claim13, wherein a fluid is disposed within the inflatable space in theinflated configuration.
 16. The implantable device of claim 15, whereinthe fluid is a liquid.
 17. The implantable device of claim 13, whereinthe smooth curved ovate projection is further configured to cause theouter side of the artery to progressively deform into the smoothlycurved oval depression, wherein the smoothly curved oval depression isdefined by a continuous line.
 18. The implantable device of claim 13,wherein the smooth curved ovate projection is configured to cause theouter side of the artery to progressively deform into the smoothlycurved oval depression without stretching a wall of the artery.
 19. Theimplantable device of claim 13, wherein the smooth curved ovalprojection is configured to result in the outer side of the arteryhaving a smoothly curved oval depression on an substantially unstretchedwall of the artery.